Author: Ohgaki, H.
Paper Title Page
TUP057 Development of Compact THz-FEL System at Kyoto University 501
  • S. Suphakul, T. Kii, H. Ohgaki, Y. Tsugamura, H. Zen
    Kyoto University, Kyoto, Japan
  • Q.K. Jia
    USTC/NSRL, Hefei, Anhui, People's Republic of China
  We are developing a compact accelerator based terahertz (THz) radiation source by free-electron laser (FEL) at the Institute of Advanced Energy, Kyoto University. The system consists of a 1.6 cell BNL type photocathode RF-gun, a focusing solenoid magnet, a magnetic bunch compressor, focusing quadrupoles and an undulator. The system generates an ultra-short electron pulse in a few hundred femtoseconds shorter than radiation wavelength, resulting in super-radiant emission from the undulator. The target radiation wavelength is 100 to 300 μm. A tracking simulation and optimization are performed by using PARMELA and General Particle Tracer (GPT) code. The FEL radiations are analyzed by a 1 dimensional FEL theory. The design parameters, simulation results and status are reported and discussed in this paper.  
TUP060 Potential Photochemical Applications of the Free Electron Laser Irradiation Technique in Living Organisms 505
  • F. Shishikura, K. Hayakawa, Y. Hayakawa, M. Inagaki, K. Nakao, K. Nogami, T. Sakai, T. Tanaka
    LEBRA, Funabashi, Japan
  • T. Kii, H. Ohgaki, H. Zen
    Kyoto University, Kyoto, Japan
  • T. Sakae
    Nihon University School of Dentistry at Matsudo, Matsudo-shi, Japan
  In 2001, the Laboratory for Electron Beam Research and Application (LEBRA) achieved the first lasing of 0.9–6.5 microns near-infrared free electron lasers (FELs), in which higher harmonics were generated by using nonlinear optical crystals. Following this breakthrough, we have paid considerable attention to LEBRA-FEL’s potential for investigating photochemical reactions in living organisms. We have established a micro-irradiation technique using an optical fiber connected to a fine tapered glass rod of <5 microns in diameter, enabling FEL irradiation of a single cell and even the inner organelles of live cells. We then verified that visible LEBRA-FEL light can control the germination of lettuce seeds, a well-known photochemical reaction, and determined that red light (660 nm FEL) promotes germination and far-red light (740 nm FEL) inhibits it. Here, we summarize the efficiency of various visible wavelengths of LEBRA-FEL light, ranging from 0.4–0.8 microns, for regulating photoreactions in lettuce seeds and we also summarize the efficiency of infrared wavelengths up to 20 microns, which can be generated by combined use of the LEBRA-FEL and the Kyoto University FEL.
We thank the staff of Prof. T. Morii (Institute of Advanced Energy, Kyoto Univ.) for helpful assistance.
Observation of Time-Resolved Phase Change in Polymer Films using a Mid-Infrared FEL  
  • T. Nakajima, E.I. Ageev, T. Kii, H. Ohgaki, H. Zen
    Kyoto University, Kyoto, Japan
  The operation wavelength of FEL at Kyoto University is 5-20μm with a macropulse duration of 1.5μs, micropulse duration of 0.6ps, and wavelength stability of <1.3% [1]. Using frequency conversion we can obtain the single-shot spectra of mid-IR FEL [2]. Toward the time-resolved (TR) study we have installed the plasma mirror to shorten the macropulse duration from μs to ns [3]. Polymers are interesting candidates for the TR study in the mid-IR region. Some of the well-known polymers are polystyrene (PS), polyethylene (PE), etc. PS exists only in an amorphous phase, while PE exists in both amorphous and crystal phases. In this study we undertake the TR study of PE films. We melt the PE film with ns laser pulses at 532 nm, and probe the following dynamics using the mid-IR FEL. To increase the absorption efficiency at 532 nm, we fabricate the PE film doped with gold nanoparticles. As a result of melting the sharp absorption peaks of PE turns to the broad peak, indicating the phase change from crystal to amorphous. This way, we can observe the phase change of PE films in a TR manner with the mid-IR FEL, which is not possible with other commonly used devices such as FTIR.
[1] Qin et al., Opt. Lett. 38, 1068 (2013).
[2] Wang, Nakajima, Zen, Kii, Ohgaki, Opt. Lett. 37, 5148 (2012).
[3] Wang, Nakajima, Zen, Kii, Ohgaki, Appl. Phys. Lett. 103, 191105 (2013).
THP045 Development of Photocachode Drive Laser System for RF Guns in KU-FEL 828
  • H. Zen, T. Kii, H. Ohgaki, S. Suphakul
    Kyoto University, Kyoto, Japan
  • R. Kuroda, Y. Taira
    AIST, Tsukuba, Ibaraki, Japan
  Funding: This research was supported by ZE Research Program, IAE, Kyoto University (ZE26A-22).
We have been developing an accelerator based infrared light sources at Institute of Advanced Energy, Kyoto University. An MIR-FEL has been developed* and a THz-FEL is under development**. A thermionic RF gun has been used as the electron source of MIR-FEL. A project of photocathode upgrade of the current thermionic RF gun is now undergoing to increase the peak power of the FEL. We need to develop multi-bunch laser for this purpose. On the other hand, the THz-FEL will be a single-pass FEL using an S-band 1.6-cell photocathode RF gun. For this purpose, a single-bunch laser is enough. A photocathode drive laser system for those purposes has been developed. The laser system consists of an Nd:YVO4 mode-locked oscillator with an integrated AOM, a laser pointing stabilizer, two diode pumped Nd:YAG amplifiers, and harmonic generators. In case of single-bunch operation of the laser, the pulse energy of higher than 150 micro-J at 266 nm has been obtained. For multi-bunch operation, 70 micro-J/micro-pulse and 70 pulses have been obtained. Optimization for multi-bunch operation of the laser is under going. In the conference, status of development of the drive laser will be presented.
*H. Zen, et al., Infrared Physics & Technology, vol. 51, pp.382-385 (2008).
**S. Suphakul, et al., in this conference.